1. Field of the Invention
The present invention relates to key locks. In particular, the present invention relates to an improved design for a key lock which provides a reversible flat key.
2. Brief Description of the Prior Art
The basic mechanism of most prior art lock cylinders consists of transverse projections displaced by insertion of the key thereby allowing rotation of the lock cylinder. It is the displacement which puts the projections in a position that permits the free rotation of the lock cylinder. There are several lock cylinders known, among which include those using "flat" keys featuring varying numbers of surface depressions of precise depths and shapes. These depressions make an accurate displacement of the projections possible as well as a large number of permutations which make them very efficient as keys.
The number of possible different combinations for a lock cylinder is determined by the number of projections and by the number of different positions which those projections may take. In theory the number of positions could be infinite, but in practice the number is limited because of the level of precision which is economical and because of the necessary play which the component elements must provide for dependable lock function.
In a flat key, the maximum variation in the positions of the projections is determined by the size of the key section. When a reversible key is used the maximum variation in the positions of the projections is reduced by one-half. This is because the tread of the sides cannot exceed one-half of the section, since the key must be reversible. To overcome this limitation prior art keys have radially placed rows of projections in the slopes. In other words, there were more than one set of projections in an angular distribution along the key.
Although this increased the possible number of combinations, it also complicated greatly the production of the lock by making it necessary to drill the lock rotor and stator in distinct steps for each set of projections. It was also necessary to assemble each projection separately and it was found that obtaining a reversible key proved to be extremely difficult.